The invention relates generally to an arrangement for processing running lengths of photosensitive material.
More particularly, the invention relates to a tank which accommodates a processing bath, e.g., a fixing or developing bath, for running lengths of photographic material or to a rack which can be removably installed in such a tank.
A known arrangement for wet processing running lengths of photographic material, e.g., running webs of photographic paper, comprises a housing, and a series of shafts mounted in the housing. A multiplicity of rollers for guiding the photographic material through the housing is mounted on each of the shafts. The shafts are arranged in such a manner that the photographic material follows a meandering or tortuous path through the housing. At least two of the rollers on each shaft have respective conveyor bands trained about the same, and the conveyor bands serve to advance the photographic material through the housing. Each of the band-engaging rollers is disposed between a pair of web-contacting rollers which engage and guide one or more webs or lengths of photographic material being drawn through the housing by the conveyor bands. The arrangement is capable of simultaneously processing several running lengths of photographic material having different widths.
An arrangement of the type outlined above is disclosed, for example, in the West German Pat. No. 31 43 201. Here, each of the web-contacting rollers is mounted on the respective shaft via a spring-loaded, automatic coupling designed in such a manner that the associated roller can rotate relative to its shaft as long as the tension in the length of photographic material being guided by the roller is below a predetermined value. When the tension in the photographic material becomes excessive, that is, exceeds the predetermined value, the roller is urged towards the shaft against the action of the springs in the coupling. The roller is thus automatically coupled to the shaft which then begins to drive the roller. The speed of rotation of the shaft exceeds the speed of advance of the photographic material which is now drawn into the housing at a rate greater than that at which it is drawn out of the housing. As a result, slack develops in the running length of photographic material and the tension is reduced. Once the tension falls below the predetermined value, the springs in the coupling urge the roller away from the shaft so that the roller becomes uncoupled and again functions as an idler roller.
The shafts are subjected to bending stresses which cause the shafts to bend. Since the bending stresses in a shaft vary longitudinally of the latter, the amount of deflection of the shaft likewise varies longitudinally of the shaft. This can cause the lengths of photographic material to shift laterally so that the photographic material is no longer transported properly. In order to compensate for the varying deflection of the shaft, the spring constants of the couplings in the arrangement of the West German patent are different at different locations of a shaft. The web-contacting rollers are accordingly displaced towards the respective shaft by different amounts when the tension in the lengths of photographic material increases beyond the predetermined value. The spring constants are selected in such a manner that the differences between the displacements of the web-contacting rollers on a shaft compensate for the varying deflection of the shaft.
A drawback of the arrangement disclosed in the West German patent is that the use of couplings having different spring constants increases the complexity and cost of the arrangement.
Furthermore, the width of the known arrangement is limited which, in turn, limits the number of lengths of photographic material that can be processed at one time. This is due to the fact that, when the width of the arrangement is increased beyond a certain point, the use of couplings having different spring constants is no longer sufficient to compensate for varying deflection of a shaft. The reason is as follows: In the arrangement of the West German patent, the photographic material is secured to the conveyor bands via clamps which are perpendicular to the direction of advance of the photographic material. A relatively large prestress exists and it has been found that, due to this prestress, the band-engaging rollers are subjected to forces up to ten times as great as those which act on the web-contacting rollers. The forces acting on the band-engaging rollers tend to urge the uppermost band-engaging rollers in the housing downwards and the lowermost band-engaging rollers upwards. In order to maximize the number of lengths of photographic material which can be processed at one time, it is necessary to place the band-engaging rollers between the web-contacting rollers. However, this increases the distance, and hence the moment arms, between the band-engaging rollers of a shaft and the bearings of the respective shaft. Consequently, the shaft is deflected to such an extent that even the use of couplings having different spring constants is unable to fully compensate for the deflection. This means that the web-contacting rollers assume and maintain inclined positions thereby leading to lateral shifting of the lengths of photographic material.
Certain apparatus have fixed shafts. In such apparatus, each roller is mounted on the respective shaft so as to be freely rotatable relative thereto under all circumstances, i.e., the shafts and the rollers are devoid of means for establishing connections between the same. Certain other apparatus are designed so that all rollers on a driven shaft are fixed to the shaft for rotation therewith. In both types of apparatus, compensation for varying deflection of a shaft evidently cannot be accomplished by means of spring-loaded couplings.
In those situations where it is not possible to compensate for varying deflection of a shaft via spring-loaded couplings, current practice is to substantially increase the diameter of the shaft, e.g., from 20 mm to 25 mm. The increased diameter reduces the variations in the deflection of the shaft. However, since the shafts in an arrangement for the wet processing of photographic materials must be composed of high-priced stainless steel, an increase in shaft diameter greatly increases the cost of the arrangement. Moreover, an increase in shaft diameter considerably increases the weight of the arrangement. This is particularly unfavorable when the arrangement takes the form of a rack which is removably installed in a processing bath because the rack becomes heavy and therefore difficult to exchange.